Such flowmeters are known in numerous embodiments. DE 3,317,923 describes such a flowmeter, termed a flow switch, that has a paddle projecting into the fluid flow to be monitored. A pivotal rod carrying the paddle has a free end carrying a permanent magnet that cooperates with a Reed switch. Thus, like numerous other similar flowmeters, this paddle forms in the flow a flow resistance. If the flow level is sufficient, it pivots the paddle in the flow direction, as a rule against the force of a spring. In most cases, this movement is converted into rotation in order to activate a mechanical display or electrical switch.
Another flowmeter having a similar construction is known from the publication Qualitrol Technical Data Sheet: Oil Flowmeter Series 092″ [Technisches Datenblatt Qualitrol: Ölströmungsmelder Serie 092], publication date: March 1992. Here as well, a mechanical actuating force is exerted on a flag (i.e. paddle) placed in the flow.
However, all currently known flowmeters of the type described above have certain disadvantages:
On the one hand, they tend to jam in their final positions for different reasons. This is often due to the fact that the mount is inadequate, the rotatable shaft is twisted, or the actuating force is not sufficient by virtue of the construction of the flowmeter. Moreover, the known flowmeters are sensitive to the turbulence often produced by pumps, such that the display wobbles or the necessary force for moving the display is not sufficient. Occasionally, nonactivation may also be found due to cavitation and turbulent, nonlaminar flow.